Conventionally, it has been known that an operation apparatus performs a pressing operation on an operation plane of an operation plate with an operator's fingertip (operation body), and outputs a detection signal according to the pressing force. The operation apparatus includes: an assembly member mounted to the operation plate; an elastic member that is arranged between the operation plate and the assembly member and is deformed elastically with the pressing force exerted by the operation body; and a sensor that detects a changing amount of the elastic deformation (elastic deformation changing amount).
Accordingly, when the changing amount of a sensor's output value is larger than or equal to a predetermined threshold value, it is determined to have a pressing operation, and then a command signal corresponding to the pressing operation such as a signal for commanding a vehicular air conditioner to start operation is outputted.
However, variation may occur in an initial deformation amount of the elastic member at an initial state in which the pressing operation is not performed. The variation is caused by the assembly tolerance of the operation plate and the assembly member. In a situation where a characteristic line, which represents a relation between the elastic deformation changing amount generated by the pressing operation (pressing amount) and the sensor's output value is illustrated as a curved line (non-linear), the variation occurs and the accuracy for determining whether it is the pressing operation becomes worsen. For example, in a situation where the characteristic lines are exemplified in FIGS. 5 and 6, the sensor changing amounts ΔS are different even when the pressing amounts ΔL are identical.